Structure Comparison of Two Coexistent Weevil Rostra on Ailanthus: The Response to Ecological Demands of Egg Deposition

Abstract

Background: Elongated rostra play an important role in the egg-laying of weevils, and its emergence is a key event in the adaptive radiation of weevils. Eucryptorrhynchus scrobiculatus Motschulsky and E. brandti Harold co-occur on the same only host Ailanthus altissima, while their oviposition sites are different. In order to understand the adaptation between the rostra of the two weevils and their oviposition sites, the structural differentiation of rostra in E. scrobiculatus and E. brandti was compared. Results: The present study reveals that: (1) The rostra length of E. scrobiculatus and E. brandti was found to be correlated with body size, larger specimens have a proportionally longer rostrum. The increased rostra length is probably a by-product of the larger body sizes. (2) There were significant differences in the external shape of the two rostra, especially the shape of the mandibles of the mouthparts at the apex of the rostra used to excavate an oviposition cavity. (3) There was no difference in the size of the abductor muscles that control the extension of the mandibles, but there were significant differences in the size of the adductor muscles that control the contraction of the mandibles. Conclusion: These structural differences reflect the functional potential ovipositional tactics of rostra, which is considered to be a response to the ecological demands of egg deposition, and also provide new insights into the coexistence of two weevil species in the same host A. altissima.